Machines used to cut or pulverize large hard objects such as concrete walls, trenches, tunnels or roadways relatively large, powerful and rugged. Many such machines employ a relatively large and rugged rotating wheel, rotor or endless chain which has a plurality of cutting bits projecting radially outwards from the periphery of the wheel. The bodies of cutting bits used in the machines to work on refractory materials are usually made of strong steel. Working surfaces of the cutting bits are generally made of an even harder material such as tungsten carbide. However, even cutting bits which are ruggedly made, as described above, are worn out or broken at a relatively rapid rate, when used to cut or grind road surfaces, concrete walls, trenches, tunnels and the like. For that reason, most rotary wheel cutters used for such applications are provided with cutting bits which may be individually replaced when worn out or broken.
Rotary wheel cutters of a particular type are also used to cut tree stumps. Typical rotary wheel stump cutters use a vertically disposed rotary wheel having a plurality of carbide tipped cutting bits which are positioned at regular circumferential intervals around the periphery of the wheel and project radially outwards from the wheel. The wheel is driven at approximately 900 rpm. by a 65 horsepower motor, and is moved horizontally into contact with a stump. The rotation axis of the wheel is then pivoted or swung back and forth in a horizontal plane. As the wheel cuts an arc-shaped swath into the stump, the machine is advanced forward and downwards into the stump, until the entire stump is cut down.
Rotary wheel stump cutters of the type described above are typified by the apparatus described in the following patents:
McCreery, U.S. Pat. No. 3,570,566, Mar. 16, 1971. Rotary Cutting Device: Discloses a stump cutter having a vertically oriented rotating disc mounted on the outer end of a swingable arm. The disc has a plurality of support blocks for cutting bits mounted about its periphery. Each support block has a bore which rotatably supports a picklike cutting bit.
Ver Ploeg, U.S. Pat. No. 3,797,544, Mar. 19, 1974. Cutter Disc: Discloses a cutter disc for stump cutting machines which has a plurality of cutter tools on opposite sides thereof and each of the tools includes a bit holder having half sections for clamping the shank of a bit therebetween in a slot formed in the mating face of one of the half sections. The mating faces of the half sections are in a plane extending at an angle to the disc such that the bit extends at an angle to the disc and radially outwardly from the disc center axis of rotation. The bit holder may be turned between two positions 180 degrees apart and the bit will extend outwardly relative to the disc in one position and inwardly relative to the disc in the other position. A pair of bolts extend through the holder half sections and the disc to connect two holders on the disc on opposite sides thereof. The depth of the slot perpendicular to the face thereof is less than the thickness of the bit shank to assure clamping action by the two half sections when drawn tightly together. The bits include a cutting head having a depth limiting shoulder such that all bits extend uniformly into the bit holders at equal distance and are limited by the shoulders engaging the outer edge of the holder.
Ver Zante & Ver Ploeg, U.S. Pat. No. 3,935,887, Feb.3, 1976 Cutter Disc: Discloses a stump cutter disc similar to the above-cited disc, but having square rather than circular plan view bit holding block half sections which are stated to require less specialized tooling for their fabrication.
British Patent 1,139,679, Powell. Jan. 8, 1969. Improvements In And Relating To Apparatus For Clearing Tree Stumps And Roots: Discloses an improvement for rotary disc stump cutters comprising a hydraulically actuated articulating arm support structure for the disc.
Some rotary wheel stump cutters of the type listed above use opposed pairs of carbide tipped cutting bits of different shapes at different circumferential locations around the periphery of a rotating, vertically disposed wheel. The cutting bits are removably attached to regularly spaced circumferential stations around the periphery of the wheel. Outward radial projection of the carbide-tipped bits from the circumference of the wheel is adjustable, and the shape and radial projection of each cutting bit is selected according to a pre-determined pattern which has been found to optimize the stump cutting operation.
In normal operation of rotary wheel stump cutters, the cutting bits are subjected to very large impact and abrading forces For that reason, cutting bits wear out rapidly, and must frequently be replaced. Replacement of cutting bits is a time consuming process, in part because the radial projection of each bit must be individually adjusted to a specified value before the bit is fastened tightly to the wheel. Also, cutting bits used in prior art stump cutters have both a positive side cutting angle and a positive top rake angle. A positive top rake angle on bits used for stump cutting is disadvantageous because chips severed from the stump tend to jam between the body of the tip and the surface of the stump being cut.
A number of prior art cutting tools, used in various applications unrelated to stump cutting, disclose cutting bits having a peripheral cutting edge formed between two surfaces intersecting at an acute angle, thereby permitting presentation of a positive rake angle with respect to a surface being cut, while being mounted in a holder having a negative rake angle. This arrangement provides clearance between the cutting bit edge and a work surface being cut. Several of the patents listed below disclose such cutting tools.
Jones, et al., U.S. Pat. No. 3,399,442, Sep. 3, 1968, Cutting Insert.
Weller, et al., U.S. Pat. No. 3,341,921, Sep. 19, 1967. Cutting Insert.
Keller U.S. Pat. No. 3,341,923. Sep. 19, 1967. Cutting Tool.
Jones, U.S. Pat. No. 3,557,416, Jan. 26, 1971, Cutting Insert.
Porat, et al., 4,367,990, Jan. 11, 1983, Cutting Insert.
Allaire, et al., U.S. Pat. No. 4,618,296. Oct. 21, 1986. Cutting Tool And Insert Therefore.
Briese, U.S. Pat. No. 4,621,955, Nov. 11, 1986, Cone Shaped Cutting Insert.
Briese, U.S. Pat. No. 4,482,916, Jul. 28, 1987. Cutting Insert Arrangement.
Shimomura, et al., U.S. Pat. No. 4,699,549, Oct. 13, 1987, Insert Rotary Cutter.
British Patent 607,770, Fear, Sep. 6, 1948, Improvements In Or Relating To Cutting Tools For Lathes And Other Machine Tools.
British Patent 2,057,939. Apr. 8, 1981. Cuming. Method Of Machining And A Rotary Cutting Tool Therefor.
British Patent 2,092,032, Aug. 11, 1982, McCreery Cutting Insert.
The present inventor is unaware of any prior art rotary wheel cutter in which positive rake angle bits are supported in negative rake angle holders. Thus, in view of the limitations of prior art rotary wheel cutters described above, the present invention was conceived of.